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So, C++ allows overloading the unary operator &(address). Are you aware of any real-world example when operator & was rightfully overloaded? And a second, more specific question, are you aware of any real-world example when operator & was rightfully overloaded while preserving address semantics? TIA
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Overloading Unary Operator: Let us consider to overload (-) unary operator. In unary operator function, no arguments should be passed. It works only with one class objects. It is a overloading of an operator operating on a single operand.
Operators that cannot be overloaded in C++ For an example the sizeof operator returns the size of the object or datatype as an operand. This is evaluated by the compiler. It cannot be evaluated during runtime. So we cannot overload it.
When unary operators are overloaded through a member function, they do not take any explicit arguments. But when overloaded by a friend function, they take one argument. When binary operators are overloaded through a member function they take one explicit argument.
One doesn't really need operator overloading in a language since they can be simulated with more verbose function calls anyway. Avoiding operator overloading in Java made the implementation and specification of Java a little simpler and it forced programmers to not abuse operators.
I've got 207 real-world examples of operator &(): Code search 1, Code search 2.
Including SafeInt<> (to get the underlying naked integer), boost::gil (apparently also to yield the raw data), Mozilla (that say "it is risky to define operator&, but, hey, we know what we're doing."), wxWidgets, Armagetron and lots of more.
It seems some use the iterator idiom &*it to get a raw reference or pointer backwards, and write *&it to get a raw reference and &it to get a raw pointer.
Notice that once your type overloads operator& and returns something different than the built-in operator, your type is not CopyConstructible anymore (in C++03 - C++0x seems to have lifted it), and so cannot be used as element-type in a Standard container anymore.
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It appears to be used in ATL, e.g http://msdn.microsoft.com/en-us/library/5s6et3yb.aspx
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I don't know of a concrete example off-hand, but I could imagine a container class where you might want to return a smart pointer or an iterator. I'm not saying this necessarily makes sense, though.
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One good reason to overload it might be to make it private, to prevent users from using it. I can't this think of any real-world example where you would want to prevent this, but it seems to be the most logical reason to overload it.
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I did it once when an object had a special-purpose smart pointer. operator& quietly 'lifted' a stack-allocated object into a heap-based smart pointer version, and this operator behaved differently once the object was inside the pointer.
I don't have the code any more, but there was a reason for it at the time. It's certainly not a decision to take lightly, this road is lined with corpses.
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